Repot houseplants only as last resort against ants

November 11, 2007|By Scott Aker, Special toThe Washington Post

Q. I put many houseplants on the deck for the summer. They have done well, but they are full of ants. How do I get rid of the ants now that it's time to bring the plants back indoors? Should I repot with fresh soil? A. The ants may have moved on, since many of the species that infest pots have the ability to move the entire colony and often do so when nearby food resources run out. Slip the plant out of the pot to see whether there is an ant colony in the roots. Repotting is the best course to deal with an ant infestation, but should be done now only as a last resort because the dwindling light and cooler temperatures are inducing a seasonal rest period in most houseplants. One approach now is to remove the plant from its pot and keep both plant and pot separated and exposed for a few hours. The ants will feel unprotected and are likely to leave the plant. Make sure that the ants have left, and return the plant to the pot after the container has been washed. The washing may help to eliminate the trails of chemicals that the ants leave as signposts back to the pot. Use enough soil to compensate for any that was lost in the process, but don't attempt to remove all the soil and replace it. Try a fresh repotting only as a last resort, because plants that are repotted in the fall are prone to root rot from winter watering. Sometimes, ants cultivate and protect other, far more serious pests, namely aphids, scale or mealybugs, which produce food for the ants. Look closely for these because if any remain, their numbers will explode when brought indoors. If the plants are seriously infested, consider replacing them. Scott Aker is a horticulturist at the U.S. National Arboretum in Washington, D.C.